Narrative:

ZLA cleared aircraft to bands intersection with multiple short dscnts of 1000 ft - 2000 ft. Captain used vertical speed mode to accomplish task. During transition to socal approach, clearance above was received. This was to be an FMC function. We were anticipating a visual approach, shortcutting the arrival. Instead of re-engaging VNAV, first the captain set 2200 ft in altitude window -- that would have been ok, but VNAV has to be engaged to read FMC altitudes. Vertical speed let the aircraft descend below (bands, 7000 ft). Duties of crew members were divided. Captain with visual, first officer with arrival, STAR and approach checklist items. Other distrs: ATIS only receives close in as does company frequency. The ability to back each other up was not there 'as usual' -- xchks of each other not done due to division of duties. Also too distraction by RA while with ZLA by king air passing 500 ft over us. Supplemental information from acn 386755: clearance: to kayoh, cross kayoh at 7000 ft, 190 KTS. Then cleared to descend eastside 2 arrival, transition to runway 19R. Aircraft B737 FMC EFIS. During transition to socal approach, clearance above was received. This was to be an FMC function. We were anticipating a visual approach, shortcutting the arrival. Instead of re-engaging VNAV first, the captain set 2200 ft in altitude window. That would have been ok, but VNAV has to be engaged to read FMC altitudes. Let the aircraft descend below (kayoh intersection 7000 ft).

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Original NASA ASRS Text

Title: AN ACR B737 FLC DSNDS BELOW THEIR XING ALT WHEN THE CAPT SELECTS THE WRONG AUTOFLT SYS MODE AND SETS THE ALT ALERTER SELECTOR BELOW THEIR XING ALT.

Narrative: ZLA CLRED ACFT TO BANDS INTXN WITH MULTIPLE SHORT DSCNTS OF 1000 FT - 2000 FT. CAPT USED VERT SPD MODE TO ACCOMPLISH TASK. DURING TRANSITION TO SOCAL APCH, CLRNC ABOVE WAS RECEIVED. THIS WAS TO BE AN FMC FUNCTION. WE WERE ANTICIPATING A VISUAL APCH, SHORTCUTTING THE ARR. INSTEAD OF RE-ENGAGING VNAV, FIRST THE CAPT SET 2200 FT IN ALT WINDOW -- THAT WOULD HAVE BEEN OK, BUT VNAV HAS TO BE ENGAGED TO READ FMC ALTS. VERT SPD LET THE ACFT DSND BELOW (BANDS, 7000 FT). DUTIES OF CREW MEMBERS WERE DIVIDED. CAPT WITH VISUAL, FO WITH ARR, STAR AND APCH CHKLIST ITEMS. OTHER DISTRS: ATIS ONLY RECEIVES CLOSE IN AS DOES COMPANY FREQ. THE ABILITY TO BACK EACH OTHER UP WAS NOT THERE 'AS USUAL' -- XCHKS OF EACH OTHER NOT DONE DUE TO DIVISION OF DUTIES. ALSO TOO DISTR BY RA WHILE WITH ZLA BY KING AIR PASSING 500 FT OVER US. SUPPLEMENTAL INFO FROM ACN 386755: CLRNC: TO KAYOH, CROSS KAYOH AT 7000 FT, 190 KTS. THEN CLRED TO DSND EASTSIDE 2 ARR, TRANSITION TO RWY 19R. ACFT B737 FMC EFIS. DURING TRANSITION TO SOCAL APCH, CLRNC ABOVE WAS RECEIVED. THIS WAS TO BE AN FMC FUNCTION. WE WERE ANTICIPATING A VISUAL APCH, SHORTCUTTING THE ARR. INSTEAD OF RE-ENGAGING VNAV FIRST, THE CAPT SET 2200 FT IN ALT WINDOW. THAT WOULD HAVE BEEN OK, BUT VNAV HAS TO BE ENGAGED TO READ FMC ALTS. LET THE ACFT DSND BELOW (KAYOH INTXN 7000 FT).

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.